The invention relates to document processing systems. More specifically, the invention concerns the reduction of stepper motor noise when reading CMC7 documents.
Banks, credit unions and other financial institutions regularly process checks, deposit slips and other types of bank documents in order to execute financial transactions efficiently. Document processing systems have therefore become quite prevalent in the industry. Typically, information will be printed on these documents in magnetic ink which can be read both by the human eye and a computer. This form of printing is read by a process termed magnetic ink character recognition (MICR). As part of the recognition process, a MICR magnetic pickup head is used to read the information printed on the document.
A commonly used font with MICR is CMC7. CMC7 documents are printed like a magnetic barcode with bars spaced at narrow and wide intervals. As characters pass in front of the MICR head, a magnetic signal is produced at the head corresponding to the information contained on the document. When reading these types of documents, the system samples the magnetic signal coming off the head at {fraction (1/1000)} of an inch intervals. This forms the basis of the waveform used for reading. This waveform is used to produce a difference waveform by making a second copy of the waveform and delaying it by {fraction (6/1000)} of an inch. This distance therefore represents a delay of six samples at the MICR head. The original waveform is then subtracted from the delayed waveform to create a difference waveform. The difference waveform is then used to produce a working sample waveform. A working sample waveform is the current difference sample minus the previous difference sample, and is the waveform used to do the actual recognition. A particular difficulty with present techniques arises from the fact that the working sample waveform at this point contains any motor noise which is present in the document processing system.
Since the MICR head reads magnetic signals, it is very sensitive to outside noise sources. This sensitivity is especially severe in cases of motor noise. If the motor cannot be placed far enough away from the MICR head aperture or shielded adequately, then the electrical noise emanating from the motor will be perceived to be sourced from the document which is being read.
The motor noise which comes from a stepper motor running at a constant speed is periodic in nature. Stepper motors rotate a shaft by energizing magnetic pole pieces. This energizing of the pole pieces causes both positive and negative excursions to the MICR head. These excursions represent the same type of signal produced by the actual document being read. While the noise coming from the motor is periodic in nature, it is not equal in magnitude for every cycle of the motor. This fact makes noise reduction more difficult. It is therefore desirable to take advantage of the periodic nature of stepper motor noise while taking into account cycle magnitude differences. It is also desirable to reduce stepper motor noise when reading CMC7 documents without relocating the motor or providing additional shielding.
In a first aspect of the invention a method for reducing stepper motor noise in a MICR document waveform includes the steps of creating a motor noise profile from the document waveform, and creating a working sample waveform from the document waveform. The method further includes the step of applying the motor noise profile to the working sample waveform to reduce stepper motor noise. The method also creates the noise profile once per document and periodically realigns the profile with the working sample waveform to take advantage of the periodic nature of the noise.